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Uh oh

Any advice? This is a project that I bought. I get this gap with the rear spar bolted in place.
 
Do you have a straight edge clamped to the rear spar? The rear spar can flex enough to cause this.

Otherwise it's not uncommon to have to shim the forward spar attach brkt.
 
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It's pretty much impossible to clamp a straight edge there with the hinges and doublers etc. anyway flexing the spar changes the relative angles but not the gap. Does anyone see a big problem just making a filler block? The gap is 0.28", which is a lot.

I am not optimistic about the intersection fairing fitting very well, but then they never do. :rolleyes:
 
It's pretty much impossible to clamp a straight edge there with the hinges and doublers etc. anyway flexing the spar changes the relative angles but not the gap. Does anyone see a big problem just making a filler block? The gap is 0.28", which is a lot.

I am not optimistic about the intersection fairing fitting very well, but then they never do. :rolleyes:

If you extend the plane of the VS spar downward, can you remake the connecting piece with the bend in a different location to eliminate the severe offset and yield a line of force that does not create a bending couple about the spacer? If the plane is forward, then you still might have a spacer, but it would be much smaller.
 
It's pretty much impossible to clamp a straight edge there with the hinges and doublers etc. anyway flexing the spar changes the relative angles but not the gap. Does anyone see a big problem just making a filler block? The gap is 0.28", which is a lot.

I am not optimistic about the intersection fairing fitting very well, but then they never do. :rolleyes:

Even if you can't clamp a straight edge there, you need to shine a laser, or use a tight string, down through all three of the hinge bracket holes before you fabricate any spacers. Also make sure the fin spar is tightly bolted to the aft bulkhead.
 
If you extend the plane of the VS spar downward, can you remake the connecting piece with the bend in a different location to eliminate the severe offset and yield a line of force that does not create a bending couple about the spacer? If the plane is forward, then you still might have a spacer, but it would be much smaller.

No I looked at that. The bend line would have to be below the top of the hstab spar. It is really off.
 
Even if you can't clamp a straight edge there, you need to shine a laser, or use a tight string, down through all three of the hinge bracket holes before you fabricate any spacers. Also make sure the fin spar is tightly bolted to the aft bulkhead.

Good idea for the string will do.
 
We had a similar (slightly smaller) gap on our RV-3, and built a spacer with the concurrance of engineering support - worked out just fine. We drilled lightening holes in the spacer to keep it from being a huge blivet.
 
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We had a similar (slightly smaller) gap on our RV-3, and built a spacer with the concurrance of engineering support - worked ut just fine. We drilled lightning holes in the spacer to keep it from being a huge blivet.
 
We had a similar (slightly smaller) gap on our RV-3, and built a spacer with the concurrance of engineering support - worked out just fine. We drilled lightening holes in the spacer to keep it from being a huge blivet.

The -6 plans mention a spacer of up to 1/8 thickness, but also give the option of making a new vertical piece (F-681 on the -6) and moving the bend location in a direction to reduce the gap.

Check if the -4 plans mention something similar.

Looking at your picture a lower bend point would probably remove over half of the gap and then a more reasonable spacer thickness would work. The F-681 part is a simple trapezoidal piece of 0.63 less than 4 x 6 inches - dead easy to fabricate.
 
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The -6 plans mention a spacer of up to 1/8 thickness, but also give the option of making a new vertical piece (F-681 on the -6) and moving the bend location in a direction to reduce the gap.

Check if the -4 plans mention something similar.

Looking at your picture a lower bend point would probably remove over half of the gap and then a more reasonable spacer thickness would work. The F-681 part is a simple trapezoidal piece of 0.63 less than 4 x 6 inches - dead easy to fabricate.

i think that is what I will do. thanks for everyone's ideas.
 
I had same issue on my -4. Unfortunately, you don't see it until everything is built and you go to mate the tail surfaces. I fabricated a stepped shim with lightening holes. I also added a couple extra fasteners to compensate for bending moments..simple engineering standard when shims are over a certain thickness. I was lazy, and probably should have made the F-681 over as other stated.
 
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